Skip to content

FACOSA

Operation

Approximates arccosine in radians for finite source magnitudes at most one.

Assembler Syntax

FACOSA.{S|D}(z) Fn(s), Fn(d)

Privilege

Unprivileged

Required CPUID flags

FP

FPTRANSA

Repeat eligibility

REP eligible

Computes the \(\operatorname{acos}(x)\) reference in radians over finite \(x\) with \(|x| \le 1\) after DAZ and writes an implementation-bounded S- or D-format approximation under the selected FPTRANSA accuracy contract.

The required FPTRANSA_ACCURACY contract is 0x0012.

Special values

  • Source \(+1\): the result is positive zero.

  • A finite source with magnitude greater than one, or either infinity, generates NV and produces the architectural default quiet NaN.

Exact anchors

  • \(\operatorname{acos}(+1) = +0\)

Required properties

  • monotonically decreasing on \([-1, 1]\)

  • result is in \([0, \pi]\)

2.75in

Encodings

FACOSA.{S|D}(z) Fn(s), Fn(d)

Format: Instruction format for FACOSA.{S|D}(z) Fn(s), Fn(d)

Format: Instruction format for FACOSA.{S|D}(z) Fn(s), Fn(d)